Field of the Invention
The invention relates to a circuit arrangement of an electric vehicle, in particular a vehicle-sided circuit arrangement of a system for inductive power transfer to the vehicle. Furthermore, the invention relates to a method of operating the named circuit arrangement. Further, the invention relates to a method of manufacturing a circuit arrangement of an electric vehicle and to an electric vehicle.
Description of Related Art
Electric vehicles, in particular a track-bound vehicle, and/or a road automobile, can be operated by electric energy which is transferred by means of an inductive power transfer. Such a vehicle may comprise a circuit arrangement, which can be a traction system or a part of a traction system of the vehicle, comprising a receiving device adapted to receive an alternating electromagnetic field and to produce an alternating electric current by electromagnetic induction. Furthermore, such a vehicle can comprise a rectifier adapted to convert an alternating current (AC) to a direct current (DC). The DC can be used to charge a traction battery or to operate an electric machine. In the latter case, the DC can be converted into an AC by means of an inverter.
The inductive power transfer is performed using two sets of e.g. three-phase windings. A first set is installed on the ground (primary windings) and can be fed by a wayside power converter (WPC). The second set of windings is installed on the vehicle. For example, the second set of windings can be attached underneath the vehicle, in the case of trams under some of its wagons. The second set of windings or, generally, the secondary side is often referred to as pick-up-arrangement or receiver. The first set of windings and the second set of windings form a high frequency transformer to transform electric energy to the vehicle. This can be done in a static state (when there is no movement of the vehicle) and in a dynamic state (when the vehicle moves).
Due to presence of a large clearance between the primary windings and the secondary windings, the operational behavior of this transformer is different than the behavior of conventional transformers which have a closed magnetic core with negligible or small air gaps. The large air gap results in smaller mutual inductive coupling and larger leakage inductances.
The leakage inductance usually acts as a series inductance with each winding of the primary windings and of the secondary windings. To be able to transfer high power levels, it is necessary to use an adequate capacitance in order to compensate the reactance of the inductors at an operating frequency of e.g. 20 kHz. The combination of the (leakage) inductance and the (compensating) capacitance forms a resonance circuit. A perfect impedance cancellation happens if impedance values of the inductance and the capacitance are chosen such that the natural resonance frequency of the resonant circuit is equal to the operating frequency. Such a resonant circuit is tuned.
Subject to temperature changes and/or aging, a tolerance of a compensating capacitance can increase. This may result in detuning of the resonant circuit, wherein the changed resonant frequency does not correspond to the operating frequency. Such a detuning deviates the overall performance and the power transfer capability of the inductive power transfer system. Also, an impedance of the secondary side reflected to the primary side of the transformer can become capacitive. This can result in a leading current with respect to the voltage in the WPC which is highly unwanted because a leading current eliminates soft switching conditions of semiconductor switches and increases their power losses considerably. Under such operation conditions, a WPC can overheat and turn off which, in turn, interrupts the needed power transfer.
U.S. Pat. No. 7,554,316 B2 discloses an inductive power transfer system comprising a primary unit, having a primary coil and an electrical drive circuitry connected to the primary coil for applying electrical drive signals thereto so as to generate an electromagnetic field. The system also comprises at least one secondary device. The secondary device is separable from the primary unit and has a secondary coil adapted to couple with said field when the secondary device is in proximity to the primary unit. In this way, power can be transferred inductively from the primary unit to the secondary device without direct electrical conductive contacts there between. The primary unit further comprises a control unit operable to cause a circuit including said primary coil to operate, during a measurement period, in an undriven resonating condition in which the application of said drive signals to said primary coil by said electrical drive circuitry is suspended so that energy stored in said circuit decays over the course of said period. Further, the primary unit comprises a decay measurement unit operable to take one or more measures of such energy decay during said period, wherein said control unit is further operable, in dependence upon said one or more energy decay measures, to control the electrical drive circuitry so as to restrict or stop inductive power transfer from the primary unit. On the secondary side, the system comprises a dummy load switch which can be controlled by a secondary control unit selectively.
US 2011/0254379 A1 shows a pick-up for an inductive power transfer system, wherein the pick-up comprises a phase detector for detecting the phase of a voltage in a primary conductive path with which the pick-up is inductively coupled in use. Furthermore, the pick-up comprises a converter allowing adjustable phase and a controller adapted to control the power transfer between the primary conductive path and a load associated with the pick-up, by controlling at least the phase angle of the converter with respect to that of the primary conductive path voltage.
WO 99/08359 A1 discloses a contactless system to magnetically transfer electric power from an input power source to a secondary load, comprising a primary energy converter connectable to the input power source and including an output inverter; a primary inductive loop connected to the output inverter, the loop including at least one turn which is compensated to unity power factor; a secondary pickup coil magnetically coupled to the primary inductive loop and compensated to unity power factor; and a secondary energy converter connected to the secondary pickup coil, the secondary energy converter including an input inverter and being connectable to the secondary load.
It is an object of the present invention to provide a circuit arrangement of an electric vehicle, in particular a vehicle-sided circuit arrangement of a system for inductive power transfer to the vehicle, and a method of operating said circuit arrangement by which an inductive power transfer to the vehicle can be optimized even in the case that electrical properties of elements of the circuit arrangement change. Further objects of the invention are to provide a method of manufacturing a circuit arrangement and to provide an electric vehicle system architecture comprising such a circuit arrangement.